Location Determination for Mobile Devices in Emergency Situations

1. A mobile communication device comprising: a radio transceiver for sending and receiving messages; and a memory coupled to a processor for storing and executing instructions to determine that a position determining subsystem is unable to provide location information for an emergency call and to execute an emergency locator component operative to: send a locator activation request for at least temporary activation of one or more of a plurality of radio transceivers of at least another mobile communication device; broadcast an emergency location request message using the radio transceiver, wherein the emergency location request message includes a unique identifier of the mobile communication device and a received signal strength indication (RSSI) value to enable the at least another mobile communication device to determine if it should respond to the emergency location request message; receive one or more emergency location response messages comprising location information of the at least one other mobile device in response to the emergency location request message, the response message including information for determining a distance estimate; and determine location information for the device based on the one or more emergency location response messages and the distance estimate.

2. The mobile communication device as claimed in claim 1 wherein the emergency locator component is further operative to: receive emergency location request messages; and send emergency location response messages in response to received emergency location request messages.

3. The mobile communication device as claimed in claim 2 further comprising a Global Positioning System (GPS) receiver capable of determining the location information of the mobile device, wherein the location information is sent in the emergency location response message in response to a received emergency location request message.

4. The mobile communication device as claimed in claim 2 wherein the emergency locator component is configured to re-broadcast received emergency location request messages if the mobile communication device cannot provide location information in response to the received request, the re-broadcast emergency location request messages further including a unique identifier of the mobile device.

5. The mobile communication device as claimed in claim 1 wherein the emergency locator component further comprises a radio control module operative to turn on the radio transceiver to broadcast the emergency location request message.

6. The mobile communication device as claimed in claim 1 further comprising an emergency locator activation radio comprising a transceiver capable of sending and receiving the locator activation requests.

7. The mobile communication device as claimed in claim 1 wherein the emergency location request message comprises a unique identifier of the mobile device.

8. The mobile communication device as claimed in claim 1 wherein the radio transceiver is a short-range radio transceiver selected from the group consisting of: a radio transceiver compatible with a IEEE 802.11 standard; a radio transceiver compatible with a Bluetooth® standard; a radio transceiver compatible with a ZigBee® standard; an infrared transceiver; a transceiver compatible with a WiMax™ standard; or an ultra wideband transceiver.

9. The mobile communication device as claimed in claim 1 wherein the response message comprises an indication of the number of mobile device hops between the mobile device and the one or more other mobile devices providing the location information.

10. The mobile communication device as claimed in claim 1 , wherein the locator activation request is sent from the device to the other mobile devices or sent from the device to a centralized server that pushes the locator activation request to the other devices.

11. The mobile communication device as claimed in claim 1 wherein the emergency locator component is further operative to: receive a further locator activation request from a further device and activate a further radio transceiver; receive emergency location request messages; and send emergency location response messages in response to received emergency location request messages.

12. A method of determining location information for a mobile communication device, the method implemented as instructions executed by a processor of the mobile communication device, the method comprising: determining that a position-determining subsystem cannot provide location information for an emergency call; sending a locator activation request for at least temporary activation of one or more of a plurality of radio transceivers of at least another mobile communication device; broadcasting an emergency location request message using a radio transceiver on the mobile communication device wherein the emergency location request message includes a unique identifier of the mobile communication device and a received signal strength indication (RSSI) value to enable the at least another mobile communication device to determine if it should respond to the emergency location request message; receiving one or more emergency location response messages from the at least another mobile device in response to the emergency location request message received on the activated radio transceivers, each of the emergency location response messages comprising external location information from the at least another mobile device and information for determining a distance estimate; and determining location information for the mobile device using the external location information received in the one or more emergency location response messages and the distance estimate.

13. The method of claim 12 wherein each emergency response message further comprises an indication of a number of mobile device hops between the mobile communication device and the other mobile communication device that has provided the location information in the emergency response message.

14. The method of claim 12 wherein determining the location of the mobile communication device comprises: determining an accuracy estimate for the location information for each of the emergency response messages; and selecting the location information with the highest accuracy estimate.

15. The method of claim 12 wherein determining the accuracy estimate comprises assigning an accuracy weighting factor to the location information for each of the mobile device hops between the mobile device and the other mobile device, the accuracy weighting factor being based on the type of radio transceiver used to receive the emergency location response message and the strength of the signal of the received emergency location response message.

16. The method of claim 12 further comprising: receiving a locator activation request using a radio transceiver; and turning on all of the radio transceivers of the mobile device.

17. An emergency locator component stored in memory and executed by a processor of a mobile communication device, the emergency locator component comprising: an emergency locator control module operative to: broadcast and receive emergency location request messages using a radio transceiver on the mobile device in response to a determination that a position-determining subsystem is unable to provide location information for an emergency call wherein the emergency location request message includes a unique identifier of the mobile communication device and a received signal strength indication (RSSI) value to enable the at least another mobile communication device to determine if it should respond to the emergency location request message; and send and receive emergency location information response messages comprising location information of mobile devices and information for determining a distance estimate; a location determination module operative to determine the location of the mobile device based at least on the location information received in emergency location information response messages and the distance estimate.

18. The emergency locator component of claim 17 , wherein the emergency locator activation radio exchanges the locator activation requests with a centralized server or with other mobile devices.

19. A system for determining a location of a mobile communication device, the system comprising: a first mobile communication device comprising: a radio transceiver for sending and receiving messages; a memory coupled to a processor for executing an emergency locator component operative to: broadcast an emergency location request message using the radio transceiver on the first mobile device wherein the emergency location request message includes a unique identifier of the mobile communication device and a received signal strength indication (RSSI) value to enable the at least another mobile communication device to determine if it should respond to the emergency location request message; receive an emergency location response message comprising location information and information for determining a distance estimate; and determine location information for the first mobile device based location information received in the emergency location response message and the distance estimate; and a second mobile communication device comprising: a Global Positioning System (GPS) receiver for determining location information of the second mobile device; a plurality of radio transceivers for sending and receiving messages; a memory coupled to a processor for executing an emergency locator component operative to: receive a locator activation request to at least temporarily activate one or more of the plurality of radio transceivers of the second mobile communication device; receive the emergency location request message from the first mobile device using one or more of the activated transceivers; determine from the unique identifier of the mobile communication device and the received signal strength indication (RSSI) value whether to respond to the emergency location request message; and if an emergency location response is to be sent in reply to the emergency location request message, send the emergency location response message comprising location information using position data from the GPS receiver as well the information for determining the distance estimate to enable the first device to determine its location.

20. The system as claimed in claim 19 wherein the first mobile communication device further comprises an emergency locator activation radio comprising a transceiver capable of sending an emergency locator activation request and wherein the second mobile communication device further comprises an emergency locator activation radio comprising a transceiver capable of receiving the emergency locator activation request from the first mobile device or from a centralized server.

21. The system as claimed in claim 19 wherein the emergency locator component in the second mobile communication device is configured to: re-broadcast the emergency location request message received from the first mobile communication device when the second mobile communication device cannot provide location information in response to the emergency location request message; receive a response message in response to re-broadcasting of the emergency location request message; and forward the response message to the first mobile communication device.